Nonequilibrium Charge Carrier Generation - Recombination Mechanisms in CdMnTe Thin Films

The absorption, photoconductivity and photoluminescence spectra of Cd0.5Mn0.5Te thin films, deposited by “flash” evaporation and vapor phase deposition have been analyzed. The energy gap and the energetic position of the recombination levels in CdMnTe thin films for different substrate temperatures have been determined. The investigation results have been compared with the same parameters for CdMnTe single crystals used as evaporation material.

Structural and Electronic Properties of Polycrystalline Cu(In,Ga)(S,Se)2 Alloys

ABSTRACTWe present a systematic study on the polycrystalline Cu(In,Ga)(S,Se)2 alloys with a gallium to indium ratio of Ga/(Ga+In)<0.3 and a sulfur to selenium ratio varying in the range between 0<S/(S+Se)<1. All samples were grown by coevaporation of the elements at constant rates under high vacuum conditions. The formation of island-like (Cu,S,Se) segregations correlate with the sulfur to selenium ratio in the layer and are found in the growth region near the copper rich phase boundary. These segregations are related to a preferred incorporation of sulfur in the copper rich growth mode. We obtain solar cell grade material from an indium rich growth mode up to a sulfur to selenium ratio of S/(S+Se)=0.9. A detailed analysis of the electronic and optical properties of Mo/CIGSSe/CdS/ZnO:Al heterojunctions allows us to determine the energetic position of the bands within the Cu(In,Ga)(S,Se)2 alloy system. We find that contrary to the Cu(In,Ga)(Se)2 alloy system the valence band position is significantly lowered with increasing bandgap.

Limits and Properties of Size Quantization Effects in InAs Self Assembled Quantum Dots

In this paper we report on the limits and properties of size quantization effects in InAs self assembled quantum dots (QDs). Size, density and character of the InAs islands are investigated by transmission electron microscopy. The electronic and optical properties of the islands in the coherent and dislocated growth regime are studied using capacitance, photoluminescence, photovoltage and photocurrent spectroscopy. In the data measured with the different techniques, the change in dot size and density as well as the transition from coherent to dislocated island growth is clearly observable. An increasing QD size causes a red shift in the energetic position of the QD features while the density of the islands is reflected in the intensity of the QD signal. The decrease in intensity at high InAs coverage is attributed to dislocated island formation.

The Effects of Impurity Codoping on the Electrical Properties of Erbium Ions in Crystalline Silicon

We have investigated the effects of oxygen codoping and thermal annealing on the deep level spectrum and carrier lifetime of Er implanted crystalline Si. It is found that oxygen codoping produces a dramatic modification in the concentration and energetic position of Er-related deep levels in the Si band gap. In particular the formation of Er-O complexes is shown to produce a promotion from deep to shallow levels. This effect is the major responsible of the enhancement of Er donor behaviour in presence of oxygen and also produces a large increase in the minority carrier lifetime